diff --git a/sylk/applications/webrtcgateway/models/firebase.py b/sylk/applications/webrtcgateway/models/firebase.py
index 0826ea5..e46e229 100644
--- a/sylk/applications/webrtcgateway/models/firebase.py
+++ b/sylk/applications/webrtcgateway/models/firebase.py
@@ -1,80 +1,82 @@
 
 from sipsimple.util import ISOTimestamp
 
 from .jsonobjects import BooleanProperty, IntegerProperty, StringProperty, ObjectProperty, FixedValueProperty, LimitedChoiceProperty, AbstractObjectProperty
 from .jsonobjects import JSONObject
 
 
 class NotificationData(JSONObject):
     body = StringProperty(optional=True)
     sound = StringProperty(optional=True)
     title = StringProperty(optional=True)
     subtitle = StringProperty(optional=True)
 
 
 class ApplicationData(JSONObject):
     sylkrtc = AbstractObjectProperty()
 
 
 class FirebaseRequest(JSONObject):
     priority = LimitedChoiceProperty(['normal', 'high'], optional=True, default='high')
     content_available = BooleanProperty(optional=True, default=True)
     time_to_live = IntegerProperty(optional=True)  # for how long should the system try to deliver the notification (default is 4 weeks)
     to = StringProperty()
     notification = ObjectProperty(NotificationData)
     data = ObjectProperty(ApplicationData)
 
     def __init__(self, token, event, **kw):
         super(FirebaseRequest, self).__init__(to=token, data=dict(sylkrtc=event), notification=event.notification, **kw)
 
 
 # Event base classes (abstract, should not be used directly)
 
 class SylkRTCEventBase(JSONObject):
     timestamp = StringProperty()
 
     def __init__(self, **kw):
         kw['timestamp'] = str(ISOTimestamp.utcnow())
         super(SylkRTCEventBase, self).__init__(**kw)
         self.notification = NotificationData(body=self.notification_body)
         if self.notification_sound is not None:
             self.notification.sound = self.notification_sound
 
     @property
     def notification_body(self):
         raise NotImplementedError
 
     notification_sound = None
 
 
 class CallEventBase(SylkRTCEventBase):
     event = None  # specified by subclass
     originator = StringProperty()
     destination = StringProperty()
 
     @property
     def notification_body(self):
         return '{0.event_description} from {0.originator}'.format(self)
 
+    notification_sound = 'default'
+
     @property
     def event_description(self):
         return self.event.replace('-', ' ').capitalize()
 
 
 # Events to use used in a FirebaseRequest
 
 class IncomingCallEvent(CallEventBase):
     event = FixedValueProperty('incoming-call')
 
 
 class MissedCallEvent(CallEventBase):
     event = FixedValueProperty('missed-call')
 
 
 class ConferenceInviteEvent(CallEventBase):
     event = FixedValueProperty('conference-invite')
     room = StringProperty()
 
     @property
     def notification_body(self):
         return '{0.event_description} from {0.originator} to room {0.room}'.format(self)